Numerous studies have demonstrated that minority patients receive poorer quality healthcare than non-minorities. Whether or not these differences in care quality are due to vulnerable patients receiving their care at facilities or from providers who provide lower quality care in general is an important question that lias been inadequately explored The study that we propose has four aims. (1) To assemble a database that combines information on a representative sample of US physicians gleaned from a representative survey, linked to information on their patients who ars enrolled in the Medicare program. (2) To assign process of care and outcome measures, to each patient by applying established and validated algorithms to these patients' Medicare claims. The processes will be oriented towards prevention; the outcomes will be potentially avoidable hospitalizations. p) To evaluate the determinants of quality at the physician level, by evaluating the association between pnysician characteristics and the care and outcomes of their individual patients. (4) To determine to what extent variations in physician quality and healthcare setting result in health disparities. This study will take advantage of information gleaned during Round 3 of the Center for Studying Health System Change Physician Survey, and also the rich data contained in Medicare inpatient and outpatient c aims databases. Using this linked database, we will assess the rates at which patients receive sub-opt mal preventive services, experience potentially avoidable hospitalizations, and the relation between their physician's characteristics and these events. We have two hypotheses. (1) That there will be large discrepancies between the characteristics of physicians treating minority patients and those treating non-minority patients, and these discrepancies will be associated with factors that predict differences in care quality. (2) When evaluated in analyses controlling for these differences in providers, most disparities in care and outcome between the patient groups will be explained. The significance of these findings would be that a singular approach to improving the quality of care provided by physicians should enhance care quality overall and reduce healthcare disparities.